Background: The use of modular tibial components in total knee
arthroplasty introduces a possible source of polyethylene wear at the
nonarticulating (backside) surface. However, it is not known whether this
phenomenon is an incidental finding observed in unique specimens or is a
feature common to all modular components. The purpose of this study was to
determine the type and severity of backside wear in retrieved tibial inserts
of several common total knee designs.
Methods: One hundred and twenty-four polyethylene tibial inserts of
twelve different designs were retrieved at revision total knee replacements
after implantation periods ranging from zero to 180 months. Each insert was
visually inspected with use of a stereomicroscope for seven different modes of
surface damage in four quadrants defining the backside surface.
Results: Pitting, burnishing, and measurable polyethylene
protrusions were observed on the backside of polyethylene inserts of implant
designs with a variety of different capture mechanisms. Across all implant
designs, pitting was observed in 90% of the retrieved specimens; burnishing,
in 77%; and protrusion, in 61%. Overall, implants of the IB-II
(Insall-Burstein-II) design (Zimmer) exhibited the most severe burnishing,
whereas those of the Duracon design (Howmedica) had the most severe pitting.
Severe protrusions were noted with inserts of one design (AMK [Anatomic
Modular Knee]; DePuy). A longer time in situ was associated with larger
polyethylene protrusions, but the severity of pitting and burnishing did not
increase with increasing duration of implantation.
Conclusions: Moderate-to-severe wear of the nonarticulating surface
of the tibial insert was frequently observed in all designs of knee
prostheses, independent of the capture mechanism. These results indicate that
new designs of modular tibial components are needed to prevent the generation
of polyethylene wear debris through backside wear of total knee
Level of Evidence: Therapeutic study, Level III-2
(retrospective cohort study). See Instructions to Authors for a complete
description of levels of evidence.